Introduction

Pyrazole derivatives are found in a diverse from natural products. They are considered as materials with biological activity and have found applications in pharmaceutical industries [1].

The diverse in bioactivity of pyrazole-based compounds have encouraged researchers to attempt to synthesize new such compounds and to study their potential biological effects. In addition, the coordinated ability for these compounds has resulted in synthesis for more complexes with different applications [2-6].

Pyrazolones are an interesting group of such ligands and have been the subject of wide investigations.

They are used as chelating agents to stabilize metal ions in difference oxidation states and to synthesize coordinated compounds with interesting features [7-10].Pyrazoline derivatives are the electron rich nitrogen heterocycles which play an important role in the diverse biological activities. These heterocyclic compounds widely occur in nature in the form of alkaloids, vitamins, pigments, and as constituents of plant and animal cell. Considerable attention has been focused on the pyrazolines and substituted pyrazolines due to their interesting biological activities.

Materials and Methods

The chemicals obtained from BDH, Merck. On a Shimadzu (FT-IR)-8400S spectrophotometer at range (4000-400 cm-1), the U.V-Vis spectrophotometer kind double beam at range (200-1000) nm, Shimadzu UV160A nm were used for characterized of synthesized compounds.  The 1H-NMR and 13C-NMR spectra of ligand were recorded on Brucker DRX kind system (500 MHz) in TMS as a standard in dimethyl sulfoxide-d6 solution. Mass spectra for ligand were recorded by (EI) mass spectroscopic using MS Model: 5973 Network Mass Selective Detector. TGA analysis of some compounds was carried out using a STAPT-1000 Linseis company, Germany. Agar diffusion was applied to test antibacterial activity.

Synthesis of bidentate ligand (L3)

This organic compound was prepared following the procedure described by Weaam A.Mahmood[11].Yellow precipitate formed which was washed with methanol and recrystallization with absolute ethanol to get a pure product and dried, melting point of ligand prepared (L3): 230-232 °C, molecular weight: 351 g/mol (C23H17N3O), Yield: 91 %.

Synthesis of bidentate ligand (L3) complexes

A solution of (0.070 g, 1 mmole) of bidentate ligand (L3) in absolute ethanol was added to a solution of CoCl2.6H2O (0.238 g, 1 mmole) in absolute ethanol. The mixture was refluxed for (1 h) with stirring. Orange precipitate was formed, which washed several time with absolute ethanol to get a pure product and dried. The similar method of Co (II) complex was synthesized. The complexes MCl2.nH2O, M (II) = [Mn(n=4),Cu (n=2) ions, Ni (n=6) ion, Zn (n=0), Cd (n=2)      and Hg (n=0) ion [12]. The physical properties of ligand (L3) complexes are presented in Table 1.

Results and Discussion

FT-IR spectrum

The important characteristic bands for FT-IR spectra of bidentate ligand (L3) and its complexes were summarized in Table 2. The FT-IR spectrum of bidentate ligand (L3), which includes a new peak at (1627) cm-1 refers to stretching frequency of azomethine group (υ C=N) [13].The bands at (1678, 1597 and 3070) cm-1 due to (C=O), (C=C) aromatic, and (C-H) aromatic stretching vibration, respectively. The FT-IR spectrum of bidentate ligand (L3) showed disappearance of two peaks of υ asy. NH2, υ sy. NH2 and band of (C=O) of anthrone and appearance of imine group indication on formation of ligand (L3) [14]. The specific peak at 1627 cm-1 which was attributed to stretching vibration of imine group (υ C=N) in IR spectrum of free ligand (L3), it is peak shifted to lower or higher frequency at range 1620-1649 cm-1 in spectra for synthesized complexes; this shift may be due to involved N atom for imine group in coordinated with metal ions [15].

Table 1: Physical properties of bidentate Schiff base (L3) complexes

Molecular formula of compounds

m.p

°C

M.Wtg/mol

found/(calc.)%

C

H

N

Cl

Metal

[Mn (C23H17N3O)2 (OH2)2]Cl2

245-247

864

63.81

4.25

9.59

7.98

6.23

(63.88)

(4.39)

(9.72)

(8.21)

(6.36)

[Co(C23H17N3O)2 (H2O)2] Cl2

 

237-239

868

63.41

4.19

9.50

7.89

6.64

(63.59)

(4.37)

(9.67)

(8.17)

(6.79)

[Ni(C23H17N3O)2(H2O)2] Cl2

238-240

867.7

63.47

4.22

9.54

7.98

6.69

(63.61)

(4.37)

(9.68)

(8.18)

(6.76)

[Cu(C23H17N3O)2(H2O)2] Cl2

 

249-251

872.5

63.10

4.16

9.45

7.91

7.15

(63.26)

(4.35)

(9.62)

(8.13)

(7.27)

[Zn(C23H17N3O)2(H2O)2] Cl2

235-237

874.4

62.96

4.28

9.46

7.87

7.28

(63.12)

(4.34)

(9.60)

(8.11)

(7.47)

[Cd(C23H17N3O)(Cl)(H2O)]C.H2O

250-252

570.4

48.25

3.50

7.21

12.27

19.51

(48.38)

(3.68)

(7.36)

(12.44)

(19.70)

[Hg(C23H17N3O) (Cl) (H2O)]Cl

234-236

640.6

42.95

2.79

6.39

10.90

31.28

(43.08)

(2.96)

(6.55)

11.08

(31.31)

 

 

The bands at range 1473-1495 cm-1 and at range 2922-2924 cm-1 are due to C=C and C-H aromatic stretching vibration, respectively. The peak at 1597 cm-1 stretching vibration, which pointing to C=N of ring of free ligand, shifted at range 1580-1591 cm-1 in the spectra for complexes, showing that coordination between N atom with metal ions had happened[16].

At the lower frequency region, the FT-IR spectra for prepared complexes revealed new peaks, not existing in spectrum for free Schiff base; these peaks appeared at 513-569 cm-1, 468-520 cm-1 due to M-N, M-O [17-18], respectively. The two bands at range 3410-3475 cm-1 and at range 819-929 cm-1 in spectra of complexes [Mn(L3)2 (H2O)2] Cl2, [Co(L3)2 (H2O)2] Cl2, [Ni(L3)2(H2O)2] Cl2, [Cu(L3)2(H2O)2] Cl2, [Zn(L3)2(H2O)2] Cl2 and [Hg(L3) (H2O) Cl]Cl are attributed to the coordinated H2O (aqua).

The band at 3412 cm-1 in spectrum of complex [Cd(L3)(H2O)(Cl)] Cl.H2O refers to H2O hydrate, while the coordinated H2O (aqua) in these complexes was confirmed by new peak at 923 cm-1 with first band at 3412 cm-1.

(C=O) amide of (L3) 1658, ν(C=N) imin 1627, ν(C=N) ring 1597, (C=O) amide of  [Mn(L3)2(H2O)2]Cl2 1658 , ν(C=N) imin 1622, ν(C=N) ring 1585, M-N 565, M-O 511, (C=O) amide of  [Co(L3)2(H2O)2]Cl2 1658, , ν(C=N) imin 1620, ν(C=N) ring 1590, M-N 513, M-O 468,  (C=O) amide of  [Ni(L3)2(H2O)2]Cl2 1658, ν(C=N) imin 1622, ν(C=N) ring 1588, M-N 569, M-O 518, (C=O) amide of  [Cu(L3)2(H2O)2]Cl 1666, ν(C=N) imin 1620, ν(C=N) ring 1591, M-N 561, M-O 513,  (C=O) amide of  [Zn(L3)2(H2O)2]Cl2 1680, ν(C=N) imin 1625, ν(C=N) ring 1585, M-N 569, M-O 520, (C=O) amide of  [Cd(L3)(H2O)(Cl)] Cl.H2O 1685, ν(C=N) imin 1633, ν(C=N) ring 1580, M-N 561, M-O 513, (C=O) amide of  Hg(L)(H2O)(Cl)] Cl 1665, ν(C=N) imin 1649, ν(C=N) ring 1585, M-N 565, M-O 511 (Table 2).

 

Table 2: FT-IR data (cm-1) of bidentate ligand (L3) complexes

Compounds

(C=O)

amide

ν(C=N)

imin

ν(C=N)

ring

M-N

M-O

L3

1658

1627

1597

---

---

[Mn(L3)2(H2O)2]Cl2

1658

1622

1585

565

511

[Co(L3)2(H2O)2]Cl2

1658

1620

1590

513

468

[Ni(L3)2(H2O)2]Cl2

1658

1622

1588

569

518

[Cu(L3)2(H2O)2]Cl2

1666

1620

1591

561

513

[Zn(L3)2(H2O)2]Cl2

1680

1625

1585

569

520

[Cd(L3)(H2O)(Cl)] Cl.H2O

1685

1633

1580

561

513

[Hg(L3)(H2O)(Cl)] Cl

1665

1649

1585

565

511

 

Electronic spectrum

The all UV-Vis spectral data of bidentate ligand (L3) and its complexes were listed in Table 3. The electronic spectrum for (L3) displayed four absorption bands. The first and second appeared at (296) nm (37175) cm-1, and also (330) nm and (30303) cm-1 were attributed to (π → π*) electronic transitions. The third and the fourth band appeared at (356) nm (28090) cm-1 and (383) nm, (26110) cm-1 were related to (n→π*) electronic transitions [19]. The electronic spectra of all complexes exhibited four absorption peaks at range 3731-2597 cm-1,which can be attributed to the intra-ligand[20]. New absorption peak at range 2681-2386 cm-1 is assigned to MLCT[21]. The new peaks in spectra of complexes Mn (II) at (419) nm (23866) cm-1, (510) nm (19608) cm-1; Co (II) at (681) nm (14684) cm-1 and (756) nm (13228) cm-1, (805) nm (12422) cm-1; Ni (II) at (416) nm (24038) cm-1, (748) nm (13369) cm-1, (981) nm (10194) cm-1 and Cu (II) at (625) nm (16000) cm-1 and (895) nm (11173) cm-1, were attributed to (d-d) electronic transitions, which indicated octahedral geometry around metal ion[22].

 

1H-NMR and 13C-NMR spectra of bidentate ligand (L3)

1H-NMR spectrum for (L3), in Figure 1 dislplays the resonances at chemical shift (δH = 6.84-8.59 ppm) are assigned to protons of aromatic ring (Ar–CH)[23]. The appearances of these protons as a multi are attributed to mutual coupling. The spectrum displayed chemical shifts at (δH = 2.49-2.50 ppm and 3.38 ppm) referred to DMSO, and the existence of water molecules HOD in the solvent respectively [24].The spectrum displayed chemical shifts at (δH = 1.47 ppm and 2.01 ppm) are assigned to protons of (CH2) group of anthrone and pyrozoline ring, respectively [23].

Figure 1: 1H-NMR spectrum for bidentate ligand (L3) in DMSO-d6

 

The 13CNMR spectrum for (L3), Figure 2, in DMSO-d6 solvent showed chemical shift at range (δ= 116.74-135.02 ppm) assignable to aromatic carbon atoms. The chemical shifts at (δ=182.95 ppm) due to the carbonyl carbon atom (C5), while the chemical shift at (δ= 156.64 ppm) due to the imine carbon atom (C26). The chemical shift at (δ=38.45 ppm and δ=32.50 ppm) attributed to the methylene group (C4, C27). The chemical shift at (δ=135.36 ppm) due to the (C7) [12].

Figure 2: 13C-NMR spectrum of bidentate ligand) L3) in DMSO-d6

 

Mass spectra of bidentate ligand (L3)

The mass spectrum for (L3) is showed in Figure 3S. The molecular ion peak of the ligand is showed at m/z+ = 351 [M]+C23H17N3O; requires = 351 (19).The other peaks detected at m/z = 239 to 51 correspond to [M1]●+ = C22H17N3O to [M15]+=C4H3. The suggested mass fragmentation of (L3) was showed in Scheme 1.

Figure 3: Mass Spectrum of bidentate ligand (L3)

                                                      

Table 3: Electronic spectral data of bidentate ligand (L3) complexes

Complexes

λ

(nm)

υ–

(cm–1)

εmax

(M-.cm-1)

Assignment

Suggested

Structure

L3

269

37175

1441

(π → π*)

 

 

 

330

30303

1000

(π → π*)

356

28090

1392

(n → π*)

383

26110

1216

(n → π*)

[Mn(L3)2(H2O)2]Cl2

269

37175

1501

Intra-ligand

Oh

315

31746

1238

Intra-ligand

368

27174

1684

Intra-ligand

383

26110

1355

Intra-ligand

419

23866

2146

MLCT  +(6A1g→4T2g (G))

510

19608

26

 (6A1g→4T1g (G))

[Co(L3)2(H2O)2]Cl2

269

37175

1453

Intra-ligand

Oh

334

29940

1253

Intra-ligand

346

28902

1736

Intra-ligand

381

26247

1298

Intra-ligand

416

24038

260

MLCT

681

14684

15

(4T1g(F) → 4T1g(P))

756

13228

4

(4T1g(F) → 4A2g(F))

805

12422

4

(4T1g(F) → 4T2g(F))

[Ni(L3)2(H2O)2]Cl2

270

37037

1638

Intra-ligand

Oh

330

30303

1500

Intra-ligand

345

28986

2341

Intra-ligand

383

26110

1528

Intra-ligand

416

24038

1990

MLCT +(3A2g(F)→3T1g(P))

748

13369

24

(3A2g(F)→3T1g(F))

981

10194

27

(3A2g(F)→3T2g(F))

[Cu(L3)2(H2O)2]Cl2

269

37175

1511

Intra-ligand

Dist.Oh

332

30120

1232

Intra-ligand

346

28902

1767

Intra-ligand

382

26178

1283

Intra-ligand

416

24038

1988

MLCT

625

16000

16

2B1g→2A1g

895

11173

49

2B1g→2B2g

[Zn(L3)2( H2O)2]Cl2

268

27313

1313

Intra-ligand

Oh

330

30303

1032

Intra-ligand

348

28736

1324

Intra-ligand

373

26810

1013

Intra-ligand+ MLCT

[Cd(L3)(H2O)(Cl)] Cl. H2O

270

37037

1667

Intra-ligand

td

328

30487

1342

Intra-ligand

346

28901

1826

Intra-ligand

385

25974

1493

Intra-ligand+ MLCT

[Hg(L3)(H2O) (Cl)] Cl

270

37037

1633

Intra-ligand

td

326

30674

1416

Intra-ligand

345

28985

1997

Intra-ligand

384

26041

1478

Intra-ligand + MLCT

 

Molar conductance

The molar conductance measurement for complexes was used to detection the ionic formula of the complexes (electrolyte or non-electrolyte). The values of molar conductivity for compounds in Dimethyl Sulfoxide (10−3M) at 25 C are listed in Table 4. The molar conductance of compounds [Mn(L3)2 (H2O)2] Cl2, [Co(L3)2 (H2O)2] Cl2, [Ni(L3)2(H2O)2] Cl2, [Cu(L3)2(H2O)2] Cl2 and [Zn(L3)2(H2O)2] Cl2 refer to 1:2 electrolytic natures. The molar conductance values of compounds [Cd (L3) (H2O) Cl]Cl.H2O and [Hg(L3) (H2O) Cl]Cl refer to 1:1 electrolytic natures.

 

Magnetic properties

The magnetic moment μeff, XM, and XA values for Mn (II), Co (II), Ni (II), and Cu (II) complex were calculated according to gramic magnetic susceptibility (Xg).

The value of diamagnetic correction Factor (D) was obtained theoretically. The μeff values of Mn (II), Co (II), Ni (II), and Cu (II) refer to octahedral geometry around metal ion. The magnetic moment of complexes were listed in Table 4.

               

Scheme 1: The suggested mass fragmentation of bidentate ligand (L3)

 

Table 4: The molar conductance of bidentate Schiff base complexes

Compounds

˄

s.cm2.mol-1

ratio

Xg×10-6

XM×10-6

XA×10-6

µeff

(B.M)

[Mn(L3)2 (H2O)2] Cl2

74.36

2:1

11.850

10238.68

10570.42

5.04

[Co(L3)2 (H2O)2] Cl2

72.51

2:1

8.615

7477.82

7809.67

4.33

[Ni(L3)2(H2O)2] Cl2

70.82

2:1

3.245

2815.69

3147.54

2.75

[Cu(L3)2(H2O)2] Cl2

71.68

2:1

1.084

945.79

1277.64

1.75

[Zn(L3)2(H2O)2] Cl2

73.42

2:1

-

-

-

0

[Cd(L3) (H2O) Cl ]Cl. H2O

40.80

1:1

-

-

-

0

[Hg(L3) (H2O) Cl ]Cl

38.32

1:1

-

-

-

0

Thermal analysis

Thermal analysis of [Ni(L3)2 (H2O)2]Cl2

The thermo gram for [Ni(L3)2               (H2O)2]Cl2 is displayed in Figure 4. In TGA, peak recognized at 122.5 °C is specific to loss for (2H2O) portions, (W.t = 0.39 mg, 4.14 %). The second step at 295.458 °C that pointing to loss for (Cl2, C6H5, CH2CO) fragment (W.t = 2. 10 mg, 21.89 %). The third step at 379. 041 °C that designated the loss of (C23H17N3O) fragment (W.t = 3.89 mg, 40.45 %). The fourth step at 889.291 °C that designated the loss of (C8H4) fragment (W.t = 1.11 mg, 11.52 %). The final remainder of the compound that appeared above 890 °C is assigned to the (NiC7H6N3), (W.t = 2.11, 21. 97 %)[25].

Figure 4: Thermal Analysis of [Ni(L3)2 (H2O)2]Cl2

 

Thermal analysis of [Cd(L3)(H2O)(Cl)]Cl. H2O

The thermo gram for [Cd(L3)                 (H2O)(Cl)]Cl. H2O is displayed in Figure 5. In TGA, peak recognized at 99.25 °C is specific to loss for (H2O) portions, (W.t = 0.16 mg, 3.15 %). The second step at 305 °C that designated the loss of (H2O, Cl2, C7H8, and 2H2) fragment (W.t = 1.70 mg, 32.45 %). The third step at 888.375 °C that designated the loss of (C16H2N2O) fragment (W.t = 2.19 mg, 41. 75 %). The final remainder of the compound that appeared above 890 °C is assigned to (CdNH3), (W.t = 1.19, 22.63 %)[26].

Figure 5: Thermal Analysis of [Cd (L3) (H2O) ( Cl)]Cl. H2O.Conclusion and suggested molecular structure for all compounds

 

According to the characterization data for new bidentate ligand (L3) and it's complexes by FT- IR, UV-Vis, (1H-NMR, 13C-NMR), magnetic susceptibility, and molar conductivity along with melting point, we found the new ligand (L3) behaves as bidentate ligand via its a N atom in imine and N atom of pyrazol ring with the central metal ions Mn (II), Co (II), Ni (II), Cu (II), Zn (II), Cd (II), and Hg (II), as shown in Figure 6. The octahedral geometrical structure was also suggested for Mn (II), Co (II), Ni (II), Cu (II), and Zn (II) complexes. Furthermore, the tetrahedral geometrical structure was suggested for Cd (II) and Hg (II) two complexes.

Figure 6: Structure of bidentate ligand (L3) and it's complexes.

 

Biological activity of ligand (L3) and its complexes

The prepared of ligand (L3) and its metal complexes of this study were tested against types of bacteria gram negative (Bacillus and Escherichia coli) and gram positive (Pseudomonas auroginosa and Staphylococcus aurus), as showed in Figures 7-10. The job of dimethyl sulfoxide in bioeffect screened was clarified by separated study conducted with the solution for dmso only, which appearance not activate as antibacterial strains [27]. The result of measured area of inhibition is indicated in Table 5.            

 

 

Table 5: Bacterial activity of bidentate ligand (L3) and its complexes

 

Compounds

Bacillus

Escherichia coli

Pseudomonas auroginosa

Staphylococcus aurus

DMSO

-

-

-

-

L3

13

20

12

12

[Mn(L3)2(H2O)2]Cl2

12

21

11

14

[Co(L3)2(H2O)2]Cl2

12

22

12

12

[Ni(L3)2(H2O)2]Cl2

14

21

15

13

[Cu(L3)2(H2O)2]Cl2

11

12

18

14

[Zn(L3)2( H2O)2]Cl2

11

11

31

15

[Cd(L3)(H2O)(Cl)] Cl.H2O

12

12

13

17

[Hg(L3)(H2O) (Cl)] Cl

12

12

26

16

 

Figure 7: Biological activity of ligand and its complexes against of Escherichia coli bacteria

Figure 8: Biological activity of ligand and its complexes against of Pseudomonas auroginosa bacteria

Figure 9: Biological activity of ligand and its complexes against of Staphylococcus aurus bacteria

Figure 10: Biological activity of ligand and its complexes against of Bacillus bacteria

 

Acknowledgments

The authors would like to express their sincere thanks with appreciation to the supervisor Prof. Dr. Sajid Mahmood Lateef. They would also like to thank the residents for the research for their efforts in correcting it.

Disclosure Statement

We have no conflicts of interest to disclose.

 

Funding

This study did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors' contributions

All authors contributed toward data analysis, drafting, and revising the paper and agreed to responsible for all the aspects of this work.

 

Conflict of interest

The authors declare that they have no conflicts of interest in this article.

 

ORCID

Weaam A. M. Al-Shammari

https://www.orcid.org/0000-0002-1026-3475

 

HOW TO CITE THIS ARTICLE

Weaam A. M. Al-Shammari, Sajid M. Lateef, Structural, Spectroscopic, Thermal, and Biological Studies of New Schiff Base Ligand Derived from Anthrone and 3-Amino-1-Phenyl-2-Pyrazoline-5-One and Its Complexes with Metallic Ions. Chem. Methodol., 2023, 7(8) 637-649

DOI: https://doi.org/10.48309/chemm.2023.404436.1687  

URL: https://www.chemmethod.com/article_178404.html